The San Diego Coroner's Office in California has confirmed she died from acute intoxication and had both alcohol and drugs in her system at the time of her death.

According to People, among the substances discovered by the coroner include methamphetamine, methadone, tramadol and nordiazepam.

The 47-year-old was found unresponsive in a parked car that blocked her driveway by a local fire department.

Speaking at the time of her half-sibling's death, Drew, 39, said: "Although I only met her briefly, I wish her and her loved ones as much peace as possible, and I'm so incredibly sorry for their loss."

Drew and Jessica's half-brother John Barrymore previously admitted he wasn't convinced she had committed suicide and correctly predicted her death was an accident.

(Photo: Facebook / Jessica Barrymore)

He said: "It looks like it was a drug misadventure. Mixing alcohol and pills. I seriously doubt she took her own life.

"There were some empty vodka bottles, a couple bags of meth and a variety of pills in the car. My guess is that it was the booze and pills, like with Heath Ledger.

"She visited her mum the day before, and her mum is almost gone. It was hard for her to see her. I doubt she tried to kill herself, though ... I predict it will be that - mixing booze and pills and taking too many."

Like her sister, Drew also had a well-publicised battle with drug and alcohol addiction in the past and went to rehab twice in her teens.

Her first role was in Stephen Spielberg's E.T. at age six. She has spoken out in the past about having her first drink at nine, began smoking marijuana at 10 and took up cocaine when she was 12. By the time she was 13 she had twice undergone drug rehabilitation treatment.

She went on to have a hugely successful career starring in Charlie's Angels

The 39-year-old Golden Globe-winning actress now runs her own cosmetics company and is a mum to two girls Frankie and Olive with husband Will Kopelman.